Alpine ski boots fitted with this type of foot-tightening device are already known. The device is provided so as to exert adjustable pressure in order to press the skier's foot against the inner wall of the shell base of the boot during skiing, in order to improve the contact between the foot and the shell base and, thus, to increase the precision with which skiing is performed. In these conventional boots, the tightening device comprises an operating lever mounted on the upper part of the shell base and capable of being adjusted to two positions: an upper, unlocking position causing the loosening of the foot within the shell base, and a lower, locking position in which the foot is tightened within the shell base. The unlocked position of the operating lever is advantageous to the skier, since it enables him to decompress his foot when he stands in a waiting line or walks in his boots. Then, when the skier lowers the operating lever into the locked position, the initial tightening of his foot is automatically restored, without having to screw or unscrew any component whatever.
Among the foot-tightening devices known to date, the one described in Applicant's Patent of Addition FR-A-2 547 487 comprises a element for exerting pressure on the foot, which extends along a slipper in which the skier's foot is inserted and which is designed to tighten this foot against the wall of the shell base. This pressure-generation element is constituted by a strap whose lower end is attached to the shell base and whose upper end is connected to a device strap tension-adjustment device. This device is constituted by a nut screwed on a threaded sleeve engaged in a manner allowing it to slide, while being unitary in rotation on an operating shaft extending horizontally and transversely within the upper part of the shell base. This operating shaft is mounted in rotation on the shell base and is connected, on the outside of the shell, to the operating lever which is articulated on the operating shaft around a pin perpendicular to this shaft. Consequently, the position of the tension-adjustment nut of the strap transverse to the shell base may be adjusted so as to change the force of the tightening stress exerted by the strap on the foot, by causing the operating shaft and lever, and consequently the threaded sleeve, to turn once this lever has been put in its upper, unlocking or loosening position.
The adjustable foot-tightening device has a major disadvantage, namely that the adjustment of tightening-stress intensity is performed by successive approximations requiring that the operating lever be preliminarily placed each time in its upper, unlocked position. In other words, when the skier wishes to adjust foot-tightness, he raises the operating lever into the upper unlocked position, then causes the operating lever and shaft to turn so as to draw the adjustment nut into a new position, and finally depresses the operating lever into the lower locking position in which his foot is tightened within the boot. If the tightening of the foot thus obtained is not suitable, he repeats the preceding operation a certain number of times until the desired tightening intensity is achieved.